What are worthwhile problems: Feynman's moving letter
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It's actually very humdrum advice. I remember reading Robert Frost's biography, and when he taught high school he coached the debate club--he told kids that, when they had some important point to make, always attribute their own words it to George Washington or so-and-so, in order to be more persuasive.
It's an annoying fact...anybody could give Feynman's advice and it would be passed over without another thought. But when words get attached to someone in authority, they are suddenly "moving".
Lin Yutang said that it was desirable in China to grow old because there is a basic rule that old people get to speak first. So something quite manifestly bad, aging, is considered good because of a rule of manners. I think that, in general, people want to become famous through science, or art, or basketball, or anything, to ennoble their own words.
You should read "Surely You're Joking, Mr. Feynman!", I [nearly] guarantee that you'll enjoy it.
Look at pg's advice on this site; a lot of it is basically "yes" or "no", and it's all highly rated, as it should be.
What else are we, at our best, but the naive ideals of our own youth? Has the world added a worthy addendum? Not in the case of yours truly, at least....
Also, his closing remarks have a lot more weight if you take in them in the context of being directly addressed from the teacher in question to the former naive, idealistic student.